1. Field of the Invention
The present invention relates generally to a novel ozone generating apparatus having a moisture exchanger, and especially one for decreasing the consumption of electric power utilized in drying a gas, such as air or oxygen, by using a dry ozone-containing gas for a recovery of adsorbent in an adsorption type air dryer.
2. Description of the Prior Art
In FIG. 1, there is shown a schematic view of a conventional ozone generating apparatus, wherein a silent discharge ozonizer 1 is connected to an air dryer 2, which uses a solid adsorbent or desiccant, such as a synthetic zeolite or a molecular sieve, active alumina, silica gel or the like, and which in turn is connected to a blower 3, as an air compressor or air blower, through a cooler 4 for the air, such as water cooling type or a freezing type cooler. Adsorption chambers 5 and 6, filled with a solid adsorbent, are disposed within the air dryer 2 being provided with three-way electromagnetic valves 7 and 8, respectively, at one end thereof and two-way electromagnetic valves 8 and 10, respectively at their other ends. A valve 11 for by-passing dry air or providing a slow leak is disposed between the respective other ends of the adsorption chambers 5 and 6 and the valves 9 and 10 thereof. An inlet pipe 12 is provided for feeding air into the dryer from the cooler 4, and an outlet gas pipe 25 is provided for discharging dry air from the air dryer to the ozonizer 1, which has an outlet pipe 26 for an ozone-containing gas of the ozonizer. The reference numerals 27 and 28 respectively designate exhaust pipes for discharging a purge gas used for a recovery of the adsorbent in the adsorption chambers 5 and 6. In the Figure, full arrow lines designate directions of flow of the air and the ozone-containing air in the conditions that the adsorption chamber 5 of the dryer is in a drying or adsorbing step and the adsorption chamber 6 is in a recovering or desorbing step, while the broken arrow lines designate the opposite directions of flow wherein adsoprtion chamber 5 is in a recovering step and the adsorption chamber 6 is in a drying step.
It is necessary to dry the air for the ozonizer 1 because improvement of the ozone generating coefficient and of the life of the ozonizer is thus attained. Accordingly, in the conventional system of FIG. 1, the air fed from the blower 3 is cooled in the air cooler 4 to a suitable degree, which is lower than a predetermined temperature of the dryer to form a dry air having a dew point lower than about -40.degree. C. in the air dryer 2, and then the air is fed to the ozonizer 1, to convert it to the ozone containing gas, and the ozone containing gas is then fed through the outlet pipe 26 to a part making use of it. The conventional air dryer for an ozonizer, which is commonly used, comprises two or more adsorption chambers being filled with a solid adsorbent which are in an automatic recovery system so that a dry air is continuously discharged while alternating the absorbing step and the adsorbent recovering step between the adsorption chambers.
As a manner of recovery of adsorbent, there are two systems, one wherein a reduced pressure-purge gas recovery system is provided in which half of each cycle is spent for adsorbing or drying under a high pressure at room temperature and half on reactivation under a reduced, or about atmospheric pressure and at room temperature purging a flow of a portion of the dried gas by-passed froom the chamber outlet in a drying step, and secondly, wherein a heating reactivation system is provided in which half of each cycle is spent for adsorbing at room temperature under atmospheric pressure and half on reactivation by heating at high temperature under ca. 1 atm., that is, a heated purge gas is passed through the adsorbent or a purge gas is passed through a heated adsorbent. The dryer for the former system is referred to as a pressure swing system dryer, or a heatless dryer, and the dryer for the latter system is referred to as a thermal swing system dryer, or a heat type dryer.
In the heatless dryer, a period of adsorption purge recovery can be decreased by about several minutes. Accordingly, the amount of the adsorbent is decreased and the size of the adsorption chamber, including the adsorption tower, can be minimized to a compact size,, and no heating is needed for reactivation or recovery of adsorbent, so that there is substantially no deterioration of the adsorbent, and it is thus advantageous with respect to the miantenance of the apparatus. However, the electric power required for drying in the heatless dryer is higher than that of the heat type dryer.
On the other hand, the heat type dryer requires less electric power for drying than does the heatless dryer. However, the heat type dryer requires a long period of adsorption-purge recovery, for example, several hours, as about 6 to 8 hours, and accordingly the size of the apparatus is large, and small amounts of organic materials in the air which are adsorbed on the surface of the adsorbent in the adsorbing step, are carbonized, polymerized or thermally decomposed, thus to deteriorate properties of the adsorbent, disadvantageously.
In the conventional ozone generating apparatus having the system of FIG. 1, a heatless dryer is used. Referring again to FIG. 1, the operation of the air drying part will now be described. First, the states of the valves and the directions of the air flow wherein the adsorption chamber 5 is in an adsorbing and drying step and the adsorption chamber 6 is in a purging and recovering step will be illustrated.
The three way valve 7 is in a closed state between pipes 13 and 27 and in an open state between pipes 13 and 15, so as to admit cool air to the adsorption chamber 5. The three way valve 8 is in a closed state between pipes 14 and 16 and in an open state between the pipe 16 and the purge gas outlet 28. The two way valve 9 is in an open state and the two way valve 10 is in a closed state. The valve 11 is set to a predetermined opening degree.
The compressed wet air fed from the pipe 12 is fed through pipe 13, through valve 7 and pipe 15 into the adsorption chamber 5, wherein the moisture is adsorbed and removed to form dry air, which then is fed to the outlet pipe 17. The dry air flow is divided here and one part is fed through the pipe 19, the two way valve 9, and the pipes 21 and 25 to the ozonizer 1 as dry air for ozone generation in a reduced pressure state, and the other part is fed through the piep 23, the valve 11, and the pipes 24 and 18 to the adsorption chambers 6 as the purge gas for a recovery of the adsorbent, in a reduced pressure state. The former is converted in the ozonizer into a dry ozone containing air which is fed through the pipe 26 or to the ozone using part or device. The latter operates to purge water from the adsorbent in the adsorption chamber 6 and to form a wet air, which is fed through the pipe 16 and the valve 8 and is then discharged from the purge gas outlet pipe 28 to the atmosphere. The directions of air flows are shown by full arrow lines. When the air flow condition is maintained for a long period, the adsorption rate in the adsorption chamber 5 increases to a super-saturated condition.
However, when a certain predetermined period, which is shorter than the period for super-saturation has passed, for example, 2 minutes, the positions of the valves are switched. The three way valve 7 then is in a closed state between the pipes 13 and 15 and in an open state between he pipes 15 and 27. The three way valve 8 is in an open state between the pipes 14 and 16 and in a closed state between the pipes 16 and 28. The valve 9 is in a closed state and the valve 10 is in an open state while the valve 11 is not changed. The wet air fed into the pipe 12 now is fed into the adsorption chamber 6, wherein water vapor is adsorbed under high pressure to dry the air. The dry air is fed to the pipe 18 wherein the dry air is divided. One part of the dry air is fed through the pipe 20, the two way valve 10 and the pipe 25 to the ozonizer 1 as the dry air for ozone generation, under a reduced pressure state. The other part is fed through the pipe 24 and the valve 11, and the pipes 23 and 17 to the adsorption chamber 5 as the purge gas for a recovery of the adsorbent under a reduced pressure state. The former is converted into the dry ozone-containing air and is fed through the pipe 26 to the ozone using part. The later is fed as the wet air from the adsorption chamber 5 through the pipe 15 and the valve 7 and is discharged from the purge gas outlet 27 to the atmosphere.
When the flow condition (the directions of air flows are shown by the broken arrow lines) is maintained for a predetermined period, such as two minutes, the valves are automatically switched so as to be in the condition wherein the adsorption chamber 5 is in an adsorbing and drying step and the adsorption chamber 6 is in a purging and recovering step. As stated above, the adsorption-purge of the adsorption chambers 5 and 6 are alternatively repeated in a constant cycle and the dry air is continuously fed into the ozonizer 1. As is clear from the illustration, in the conventional ozone generating apparatus shown in FIG. 1, it is necessary to feed not only an amount of air to the ozonizer 1 but also an amount of air for a recovery of the adsorbent into the air dryer 2. The problem is the same as that in the case of the heat type dryer.
In the embodiment of FIG. 1, it is necessary to design the adsorption chambers so as to dry all amounts of air fed into the dryer 2. In general, the cost of an ozone generating apparatus and the cost of operation are approximately similar to the total of the cost for drying raw air and the cost for the ozonizer 1. The proportion of the former cost for drying air among the total cost is high. In the case of operating cost, for example, providing the electric discharge power for feeding air in the ozonizer is 1, the electric power for drying the air is about 0.7 in the case of heatless dryers and about 0.4 in the case of heat type dryers.